There is nothing the media like to show more than pictures of huge icebergs calving from Antarctic ice shelves. Not infrequently, such large icebergs break into multiple pieces, and the question is often why, especially given that the icebergs are hundreds of meters thick.
Most icebergs that calve from the Antarctic's Ross Ice Shelf are carried by shore-hugging currents past Cape Adare, a section of coast that is south of New Zealand. In October 2005, iceberg B15A (the largest remnant of a 300-meter thick berg the size of Connecticut that broke off the Ross Ice Shelf in 2000), which had had a seismometer, compass, and GPS equipment installed in 2003 and 2004, showed the berg came to a stop, rotated back and forth a few degrees, and began cracking and splintering.
The reason? Sonar surveys found a 9KM long, previously unknown, undersea ridge where the berg broke up. The ridge was at a depth of 215 meters and was in the middle of the path traversed by coast-hugging currents in the region. Because of its depth, ships were not at risk, nor were small icebergs. But, huge bergs, like B15A, were.
As with all things scientific, it pays to not speculate too much, but to investigate. Thus, it was not warm currents that were causing the sudden breaking up of these bergs, but a good old fashion collision with an underseas ridge.
The study can be found at http://www.agu.org/pubs/crossref/2010/2009JB006700.shtml.